Plasma processing of semiconductor workpieces involves the performance of one or more plasma processes such as gas chemistry etching, gas chemistry deposition, physical sputtering, or rapid thermal annealing on one or more semiconductor workpieces/wafers within the plasma chamber. As the geometries of semiconductor devices become ever so smaller, the ability to maintain the uniformity and accuracy of critical dimensions becomes strained. Many of the processes carried out within semiconductor processing reactors leave contaminant deposits throughout the process chamber which accumulate and become the source of particulate matter harmful to the creation of a semiconductor device. As these processes become ever faster and the dimension size of the semiconductor device has become ever smaller, the presence of particulate matter upon the surface of the semiconductor workpiece has become more of a risk factor. Consequently, the cleanliness of plasma processing chambers (i.e. plasma etching, reactive ion etching (RIE), plasma enhanced chemical vapor deposition (PECVD), etc.) is critical.
Particulate contamination buildup on all the elements of the semiconductor process chamber has long been a major problem in etch processing of semiconductor elements employing metal films. These metal films are generally etched by employing a number of reactive gases, including halocarbon gases, as plasma components. In the case of an aluminum film, the etchant gases used are predominantly the chlorine containing gases, chlorine (Cl.sub.2) and boron trichloride (BCl.sub.3), which enables formation of volatile aluminum chloride compounds upon etching, which volatile compounds can be removed from the etch processing chamber by applied vacuum. However, simultaneously with the formation of volatile aluminum chloride compounds, other active chlorine and boron containing species are formed which can react with any oxygen and water vapor present in the etch processing chamber or with organic species from patterning photoresist to form non volatile particulate compositions which ultimately produce relatively large quantities of contaminant on the process chamber inner walls. The non volatile particulate compositions initially tend to remain inside the etch chamber in the form of loosely attached particles to the various element surfaces of the chamber. These contaminant compounds accumulate on the workpiece pedestal among other surfaces in the chamber.
Removal of contaminants from the various surfaces inside a plasma processing chamber has been accomplished by periodically cleaning the chamber including the workpiece pedestal and the gas distribution plates. Known cleaning methods have involved opening the plasma chamber, disassembling portions of the chamber, and removing the contaminant deposits by physical or chemical methods. For example, the chamber and the elements therein can be rinsed with a solution of hydrochloric acid, or hand wiped with a solvent, to dissolve various contaminants. Alternatively they may be washed with water and dried. All of these cleaning methods are complicated, disruptive, time consuming and can be the source of additional contamination. The problem of reactor contamination becomes particularly acute in single wafer plasma etch reactors where continuous processes are employed resulting in accumulated contaminant buildup.
One of the plasma process chamber elements which can suffer from deposition of non-volatile contaminants is the electrostatic chuck. Electrostatic chucks are devices which have gained wide usage in the semiconductor field for holding or clamping semiconductor wafers during plasma manufacturing processes. An electrostatic chuck secures the entire lower surface of a workpiece substrate by Coulombic force and provides an alternative to mechanical clamping of the workpiece to the support platform or pedestal. When a workpiece/substrate is secured to the platform using an electrostatic chuck, the flatness of the substrate/workpiece is improved. These chucks eliminate the need for mechanical clamping mechanisms, which are often clumsy and induce contamination into the processing chamber. Typical electrostatic chucks utilized in the prior art can be found in U.S. Pat. Nos. 4,184,188 (Briglia); 4,384,918 (Abe); 4,724,510 (Wicker et al.); 4,665,463 (Ward et al.); 5,166,856 (Liporate et al.); and 5,191,506 (Logan et al.).
An electrostatic chuck is a capacitor element comprised of a conductor/insulator coating structure to generate an electrostatic field between a workpiece wafer and the chuck to hold or clamp the wafer against the chuck. Various insulating coatings have been employed in these chucks including soft synthetic resins such as polytetrafluoroethylene, and polyimides or hard ceramics such as alumina or diamond. It has been found that the buildup of non volatile particulate contaminants on either hard or soft electrostatic chucks is detrimental to the holding capacity of the chuck because the presence of the particles prevents the secure seating of the lower surface of the wafer on the particle ridden surface of the chuck. Moreover, when a hard ceramic chuck is employed, accumulated contaminant particles thereon will become pulverized by continued wafer/workpiece processing and thereby form an electrically disruptive powdered coating on the insulating surface of the chuck. In the case of soft resin chucks, continued workpiece processing causes the accumulated particles on the insulating surface to be imbedded in the soft resin therein thereby disrupting the Coulombic forces generated by the chuck capacitor. Consequently, employment of electrostatic chucks in plasma processing requires that non volatile contaminants be removed by either periodically cleaning the plasma reactor or some means of control of contaminant buildup on the chuck during continuous plasma processing cycles so as to prevent undesirable contaminant buildup.
The present invention provides methods for cleaning electrostatic chucks used in semiconductor plasma treatment reactors and for controlling contaminant buildup on electrostatic chucks in continuous plasma process reactors for purposes of preventing faulty etching of improperly clamped workpieces and reducing the need to shut down and clean the plasma chamber. The present electrostatic chuck cleaning developments extend the periods of required cleaning of electrostatic chucks and particularly improves the efficiency of reactive ion etch processes.